Gary Cooper and Ernest Hemingway, two models of American virility, had similarities, not least as outdoorsmen: Cooper grew up on a farm in Montana, and Hemingway was a big-game hunter and deep-sea fisherman. But they were also a study in contrasts: Cooper worked with movie crews; Hemingway labored alone. Cooper was understated and conservative, Hemingway volatile and a liberal. The mix, as John Mulholland’s exhaustive documentary “Cooper & Hemingway: The True Gen” demonstrates, made for a friendship spanning decades.

“The true gen” (Hemingway’s military shorthand for “genuine information”) suggests Cooper’s economical acting style, which dovetailed with Hemingway’s less-is-more writing philosophy. Cooper had starred in Hollywood’s adaptation of Hemingway’s “Farewell to Arms” (1932) before the men first met in Idaho in 1940. Hemingway later insisted that Cooper be cast in “For Whom the Bell Tolls” (1943). After a critical and commercial decline, each rebounded in 1952, Cooper with “High Noon” (for which he won his second Oscar) and Hemingway with “The Old Man and the Sea” (and, two years later, his Nobel Prize). They died weeks apart in 1961.

It’s hard to think of a missing eyewitness here; some speakers — George Plimpton, Elmore Leonard, Patricia Neal — seem to return from the dead. In its allegiance to detail, the film is too long and perhaps overstates its case in claiming that later generations have lost an understanding of common courage, as depicted by these two artists. Their work endures, and so does what they stood for.